This invention relates to an improved process for hydroformylating an olefin with carbon monoxide and hydrogen in the presence of a rhodium catalyst.
Methods for producing aldehydes by the hydroformylation of an olefinically unsaturated organic compound with carbon monoxide and hydrogen in the presence of a rhodium-phosphorus complex catalyst and free phosphorus ligand are well known in the art as seen; e.g. by the basic low pressure oxo hydroformylation process of U.S. Pat. No. 3,527,809 and the rhodium-catalyzed liquid recycle hydroformylation process of U.S. Pat. No. 4,148,830.
In U.S. Pat. No. 4,148,830 issued Apr. 10, 1979, (the '830 Patent) it is disclosed that catalyst life can be enhanced and product yield improved by employing as a catalyst solvent for rhodium-catalyzed hydroformylation (or the "oxo" process), higher boiling aldehyde condensation products as defined therein. It was also found that the rhodium catalyst could be continuously or intermittently recycled to the hydroformylation reaction zone without significant loss of rhodium, catalyst life, reaction rates and efficiency.
Accordingly, the '830 Patent disclosed that liquid effluent from the reaction zone containing catalyst, solvent and gases, is processed to strip and recover the aldehyde product. During this procedure some hydrogen, carbon monoxide, unreacted olefin, and other by-product and inert gases dissolved in the reactor effluent are removed by reducing pressure on the effluent stream to flash off such gases. The desired aldehyde product is then recovered from said effluent and the liquid residue fraction of unrecovered aldehydic product, catalyst and high boiling condensation product is recycled to the reactor. Accordingly, this process has sometimes been referred to as a liquid-recycle hydroformylation process (or "liquid recycle process").
U.S. Pat. No. 4,247,486, issued Jan. 27, 1981 (the '486 Patent), discloses a hydroformylation process which is directed to further modifications of the basic oxo process disclosed in U.S. Pat. Nos. 3,527,809 and 4,148,830.
In this process, unreacted feed, the aldehyde reaction product and higher boiling condensation products, inter alia, are allowed to distill out of the reaction medium. The aldehyde product and condensation products are condensed from the gas recycle stream and unreacted feed contained therein (i.e., syn gas and olefin) are recycled to the reaction zone. This process is a gas recycle hydroformylation process or, simply, "a gas-recycle process."
U.S. Pat. No. 4,247,486 discloses that a by-product of such a recycle hydroformylation process is saturated alkane formed by the hydrogenation of the olefin. Thus, for example, propane is a by-product in the hydroformylation of propylene. Accordingly, a purge stream is taken from a gas recycle stream therein to remove such propane and to control its concentration within the process. The purge stream also contains, inter alia, aldehyde product, unreacted olefin, inert gases, as well as carbon monoxide and hydrogen. It is said in the '486 Patent that the recovery of olefin from such a stream is impractical and that the purge stream is typically used as a fuel.
Likewise, to control total reactor pressure in a liquid recycle process due to build up of inerts and the like, a gaseous purge is generally taken from the liquid recycle hydroformylation reactor, where excess hydrogen, carbon monoxide, unreacted olefin, inerts and alkane by-products, such as propane, are vented as off-gases.
In addition, during the product separation step in a liquid recycle process, some gases, primarily unreacted olefin and alkane by-product, which remain dissolved in the liquid catalyst-containing effluent, are separated along with the desired aldehyde product. A portion of such separated gases are condensed with the desired aldehyde product. The remaining separated gases can be purged from the system.
The amount of olefin and syn gas components lost by purging in such recycle processes can amount to a significant economic disadvantage over the life of a commercial continuous operation due to the efficiency loss of such purged desirables as unreacted olefin and syn gas.
In German Pat. No. 3,102,281, issued Dec. 23, 1982, a cobalt-catalyzed high pressure hydroformylation of propylene was conducted and the waste gas, resulting from the decobalting of the reaction mix, containing propylene, carbon monoxide and hydrogen, was introduced into a low pressure rhodium catalyzed hydroformylation process, simultaneously conducted. In German Laid-Open Patent No. 3,245,883, published June 14, 1984, flue gas from a low pressure rhodium hydroformylation process containing propylene is compressed and introduced into a high pressure cobalt catalyzed reactor for conversion to aldehyde.